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| United States Patent |
5,703,151
|
|
Yamamoto
, et al.
|
December 30, 1997
|
Rubber composition
Abstract
Provided is a rubber composition obtainable by kneading a mixture at a
maximum temperature between about 120.degree. to about 170.degree. C. The
mixture includes:
100 parts by weight of a solution polymerized diene rubber;
about 5 to about 100 parts by weight of silica;
about 1 to about 15 parts by weight of a silane coupling agent; and
about 1 to about 15 parts by weight of a polyalkylene glycol having a
weight average molecular weight of about 200 to about 20,000.
The invention also provides a method for making the rubber composition, a
tire tread made from the rubber composition, and a tire made from the
rubber composition.
| Inventors:
|
Yamamoto; Keisaku (Ichihara, JP);
Wakatsuki; Kizuku (Ichihara, JP);
Saba; Hayato (Funabashi, JP)
|
| Assignee:
|
Sumitomo Chemical Company, Limited (Osaka, JP)
|
| Appl. No.:
|
632798 |
| Filed:
|
April 17, 1996 |
Foreign Application Priority Data
| Current U.S. Class: |
524/262; 524/269; 524/377; 524/575 |
| Intern'l Class: |
C08K 005/24 |
| Field of Search: |
524/377,571,575,262,269
|
References Cited
U.S. Patent Documents
| 3768537 | Oct., 1973 | Hess et al. | 524/571.
|
| 3873489 | Mar., 1975 | Thurn et al. | 524/267.
|
| 4192790 | Mar., 1980 | McKinstry et al. | 524/571.
|
| 4386181 | May., 1983 | Kotani et al. | 524/377.
|
| 5091471 | Feb., 1992 | Graves et al. | 525/89.
|
| 5409969 | Apr., 1995 | Hamada.
| |
| 5496883 | Mar., 1996 | Hamada.
| |
| Foreign Patent Documents |
| 03252431 A | Nov., 1991 | JP.
| |
Other References
Haehl & Montu, `Influence Des Polyethyleneglycols Sur Le Renforcement Des
Elastomeres Par Les Silices Et Les Aluminosilicates`, vol. 39, No. 11, pp.
1727-1737 (1962).
|
Primary Examiner: Sweet; Mark D.
Attorney, Agent or Firm: Cushman Darby & Cushman IP Group of Pillsbury Madison & Sutro, LLP
Claims
What is claimed is:
1. A rubber composition obtainable by kneading a mixture at a maximum
temperature between about 120.degree. to about 170.degree. C., said
mixture comprising:
100 parts by weight of a solution-polymerized styrene-butadiene rubber
having a Mooney viscosity (ML.sub.1+4 125.degree. C.) in a range of from
about 40 to about 140;
about 5 to about 100 parts by weight of silica;
about 1 to about 15 parts by weight of a silane coupling agent; and
about 1 to about 15 parts by weight of a polyalkylene glycol having a
weight average molecular weight of about 200 to about 20,000.
2. The rubber composition according to claim 1, said silane coupling agent
is at least one selected from the group consisting of the compounds
represented by the following formulae (1) and (2):
›(OR).sub.3 SiC.sub.a H.sub.2a !.sub.2 S.sub.b ( 1)
(OR).sub.3 SiC.sub.a H.sub.2a Z (2)
wherein,
R represents a methyl group or an ethyl group;
a represents an integer of 1 to about 6;
b represents an integer of 1 to about 6; and
Z represents a mercapto group, an epoxy group, a vinyl group or an amino
group.
3. The rubber composition according to claim 1, wherein said rubber
composition exhibits the combination of properties of:
(1) improved wet-skid resistance;
(2) improved rolling resistance; and
(3) improved processability when suitably vulcanized.
4. A process for producing a rubber composition which comprises the steps
of:
kneading a mixture comprising:
100 parts by weight of a solution-polymerized styrene-butadiene rubber
having a Mooney viscosity (ML.sub.1+4 125.degree. C.) in a range of from
about 40 to about 140;
about 5 to about 100 parts by weight of silica;
about 1 to about 15 parts by weight of a silane coupling agent; and
about 1 to about 15 parts by weight of a polyalkylene glycol having a
weight average molecular weight of about 200 to about 20,000,
at a temperature in which the maximum temperature during the kneading is
between about 120.degree. and about 170.degree. C.
5. A tire tread comprising a vulcanized rubber composition having the
combination of properties of:
(1) improved wet-skid resistance;
(2) improved rolling resistance; and
(3) improved processability when suitably vulcanized,
wherein said rubber composition being obtainable by kneading a mixture at a
maximum temperature between about 120.degree. to about 170.degree. C.,
said mixture comprising:
100 parts by weight of a solution-polymerized styrene-butadiene rubber
having a Mooney viscosity (ML.sub.1+4 125.degree. C.) in a range of from
about 40 to about 140;
about 5 to about 100 parts by weight of silica;
about 1 to about 15 parts by weight of a silane coupling agent; and
about 1 to about 15 parts by weight of a polyalkylene glycol having a
weight average molecular weight of about 200 to about 20,000.
6. A tire comprising the tire tread according to claim 4.
7. The rubber composition according to claim 1, wherein the Mooney
viscosity is in a range of from about 50 to about 120.
8. The process according to claim 4, wherein the Mooney viscosity is in a
range of from about 50 to about 120.
9. The tire tread according to claim 5, wherein the Mooney viscosity is in
a range of from about 50 to about 120.
Description
1. FIELD OF THE INVENTION
The present invention relates to a rubber composition. More precisely, the
present invention relates to a rubber composition which has significantly
improved wet-skid resistance and rolling resistance in combination with
excellent processability when converted into a vulcanized rubber because
of the absence of bleeding on the surface.
2. BACKGROUND OF THE INVENTION
Rubber compositions containing silica and a silane coupling agent have been
widely used for colored or white rubbers because that they are easily
colored, compared with rubber compositions containing carbon black. These
types of rubber composition have also been used for tires because, in
general, they have a smaller loss in energy in the temperature range of
room temperature or more. The rubber compositions containing silica and a
silane coupling agent, however, exhibit problems that they have
insufficient wet-skid resistance and rolling resistance, in combination
with poor processability when converted into vulcanized rubbers.
There is a need for a rubber composition containing silica and a silane
coupling agent, which has the combination of properties of:
(1) improved wet-skid resistance,
(2) improved rolling resistance, and
(3) improved processability when converted into vulcanized rubber.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide an improved rubber
composition containing silica and a silane coupling agent which solves the
problems of conventional rubber composition containing silica and a silane
coupling agent.
As the result of extensive studies for such a rubber composition, the
present inventors have found that rubber compositions obtainable by
kneading a specific polyalkylene glycol into a solution polymerized diene
rubber containing silica and a silane coupling agent at a specific
temperature have sufficiently improved wet-skid resistance and rolling
resistance when converted into vulcanized rubbers, and are excellent in
processability because of the absence of bleeding on surface when
converted into vulcanized rubbers.
Accordingly, the present invention provides a rubber composition obtainable
by kneading a mixture comprising:
100 parts by weight of a solution polymerized diene rubber (A),
about 5 to about 100 parts by weight of silica (B),
about 1 to about 15 parts by weight of a silane coupling agent (C); and
about 1 to about 15 parts by weight of a polyalkylene glycol (D) having a
weight average molecular weight of about 200 to about 20,000,
wherein the maximum temperature during kneading is between about
120.degree. and about 170.degree. C.
The present invention also provides a method of making the rubber
composition, a tire tread made from the rubber composition, and a tire
made from the rubber composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in more detail by the following.
The component (A) in the present invention is a solution polymerized diene
rubber. While the precise structure of the solution polymerized diene
rubbers is not particularly limited, the rubbers in general have a Mooney
viscosity (ML.sub.1+4 125.degree. C.) preferably of about 40 to about 140
and more preferably of about 50 to about 120, from the viewpoint of
kneading processability. The component (A) can be obtained by any
well-known solution-polymerization method which comprises polymerizing
dienes in a solvent such as hydrocarbons and the like using an initiator
such as a organolithium compound. Also from the viewpoint of kneading
processability, the solution polymerized rubbers are preferably produced
in the presence of a coupling agent such as SiCl.sub.4, SnCl.sub.4 or the
like in solution polymerization so that a portion or the whole of the
polymers present in the solution polyeriztion contain a branched
component. Specific examples of the solution polymerized diene rubber
include:
a solution polymerized butadiene rubber (BR),
a solution polymerized styrene-butadiene rubber (SBR),
a solution polymerized isoprene rubber (IR), and the like. From the
viewpoint of tire use, a solution polymerized butadiene rubber and a
solution polymerized styrene-butadiene rubber are preferred and a solution
polymerized styrene-butadiene rubber is more preferred. These rubbers may
be used independently or in combination thereof.
The component (B) in the present invention is silica. There are various
kinds of silica which are different based on the concentration of the
surface hydroxyl group, pH and particle properties. While the silica used
in the present invention is not limited, a silica having an amount of DBA
(dibutylamine) absorption of about 100 to about 400 mmol/kg, BET specific
surface area of about 50 to about 300 m.sup.2 /g, and pH of about 5 to
about 12 is preferred.
The amount of the component (B) in the rubber composition of the present
invention is about 5 to about 100 parts by weight, preferably about 30 to
about 90 parts by weight per 100 parts by weight of the component (A). If
the amount of the component (B) is too small, the mechanical strength,
such as the tear strength, of the vulcanized rubber may be reduced. When
the amount of the component (B) is too much, the kneading processability
and mechanical strength of the vulcanized rubber may be reduced.
The component (C) in the present invention is a silane coupling agent.
Specific examples of the silane coupling agent include compounds
represented by the formulae (1) or (2) shown below. These compounds may be
used independently or in combination thereof.
›(OR).sub.3 SiC.sub.a H.sub.2a !.sub.2 S.sub.b (1)
(OR).sub.3 SiC.sub.a H.sub.2a Z (2)
In the above formulae, R represents a methyl group or an ethyl group. The
ethyl group is preferred. "a" represents an integer of 1 to about 6 and
preferably an integer of 2 to 5. "b" represents an integer of 1 to about 6
and preferably an integer of 2 to 5. "Z" represents a mercapto group, an
epoxy group, a vinyl group or an amino group.
Suitable examples of the compounds represented by the formula (1) include:
bis(trimethoxysilylmethyl) disulfide,
bis(2-trimethoxysilylethyl) disulfide,
bis(2-trimethoxysilylethyl) tetrasulfide,
bis(2-trimethoxysilylethyl) pentasulfide,
bis(2-trimethoxysilylethyl) hexasulfide,
bis(3-trimethoxysilylpropyl) disulfide,
bis(3-trimethoxysilylpropyl) trisulfide,
bis(3-trimethoxysilylpropyl) tetrasulfide,
bis(3-trimethoxysilylpropyl) pentasulfide,
bis(3-trimethoxysilylpropyl) hexasulfide,
bis(4-trimethoxysilylbutyl) tetrasulfide,
compounds in which the methoxy group in the above listed compounds is
replaced by an ethoxy group, and the like.
Suitable examples of the compounds represented by the formula (2) include:
1-mercapto-2-trimethoxysilylethane,
1-mercapto-3-trimethoxysilylpropane,
1-mercapto-4-trimethoxysilylbutane,
1,2-epoxy-3-trimethoxysilylpropane,
1,2-epoxy-4-trimethoxysilylbutane,
3-trimethoxysilyl-1-propene,
4-trimethoxysilyl-1-butene,
1-dimethylamino-2-trimethoxysilylethane,
1-dimethylamino-3-trimethoxysilylpropane,
1-dimethylamino-4-trimethoxysilylbutane,
compounds in which the methoxy group in the above listed compounds is
replaced by an ethoxy group, and the like.
Among the compounds represented by the formulae (1) or (2),
bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl)
tetrasulfide, and bis(3-triethoxysilylpropyl) pentasulfide are preferred.
The amount of the component (C) in the rubber composition of the present
invention is about 1 to about 15 parts by weight, preferably about 2 to
about 10 parts by weight per 100 parts by weight of the component (A). If
the amount of the component (C) is too small, the vulcanization velocity
and the mechanical strength of the vulcanized rubber may be reduced. When
the amount is too much, the mechanical strength may be reduced and the
production cost may be increased. When two or more of the compounds are
used as the component (C), the amount of component (C) is considered to be
the total amount of all the compounds used as the component (C).
The component (D) in the present invention is a polyalkylene glycol having
a weight average molecular weight of about 200 to about 20,000. The weight
average molecular weight of the component (D) is preferably about 250 to
about 10,000 and more preferably about 300 to about 8,000. Specific
examples of suitable polyalkylene glycols include:
polyethylene glycol,
polypropylene glycol,
an ethylene oxide-propylene oxide random copolymer,
an ethylene oxide-propylene oxide block copolymer,
and the like. If the weight average molecular weight of the component (D)
is too small, adhesion failure due to bleed may occur on the surface of
the vulcanized rubber. When the molecular weight is too large, the
wet-skid resistance and rolling resistance may be insufficient and
blooming may occur on the surface of the vulcanized rubber.
The amount of the component (D) in the rubber composition of the present
invention is about 1 to about 15 parts by weight, preferably about 1 to
about 12 parts by weight per 100 parts by weight of the component (A). If
the amount of the component (D) is too small, the effects of improved
wet-skid resistance or rolling resistance may be reduced. When the amount
is too much, the mechanical strength or abrasion resistance may be reduced
and bleeding on the surface of the vulcanized rubber may occur. Bleeding
on the surface of the vulcanized rubber can result in adhesion failure
between the vulcanized rubber comprising the composition of the present
invention and another material.
The rubber composition of the present invention can be obtained by kneading
the predetermined amounts of the components (A)-(D) as described above
under conditions in which the maximum temperature during the kneading is
between about 120.degree. and about 170.degree. C. If the temperature is
too low, the mechanical strength of the vulcanized rubber may be reduced.
When the temperature is too high, deterioration of the vulcanized rubber
may occur. The minimum temperature during the kneading should be at least
about 0.degree. C., preferably at least about 20.degree. C. If the minimum
temperature is too low, molecular chain scission of component (A) in the
first stage of the kneading may occur and the economical efficiency may be
reduced because the kneading time until the maximum temperature becomes
long. The kneading may be performed by using a conventional kneading
machine, such as rolls, a Banbury mixer, or the like, until the components
are uniformly mixed. In kneading, a common general rubber such as a
natural rubber, an emulsion polymerized butadiene rubber, an emulsion
polymerized styrene-butadiene rubber, and the like, carbon black, an
antioxidant, a processing aid, stearic acid, a reinforcing agent, a
filler, a plasticizer, a softening agent and the like may be added in
addition to the components (A)-(D).
When the above general rubber, other than the component (A), is added to
the rubber composition of the present invention, the weight ratio of the
general rubber to the component (A) is preferably about 0.6:1 or less and
more preferably about 0.45:1 or less. If the weight ratio of the general
rubber is too large, the effects of improved wet-skid resistance and
rolling resistance may be reduced.
When carbon black is added to the rubber composition of the present
invention, it is preferred to use carbon black having an iodine adsorption
of about 60 mg/g or more and a dibutyl phthalate oil absorption of about
80 ml/100 g or more. The carbon black, for example, can be used in an
amount preferably of about 100 parts by weight or less, and more
preferably of about 60 parts by weight or less, per 100 parts by weight of
the component (A).
The unvulcanized rubber obtainable by kneading the rubber composition of
the present invention can be converted into a vulcanized rubber by
vulcanizing preferably at about 100 to about 250.degree. C. and more
preferably at about 130.degree. to about 200.degree. C.
As the vulcanization agent, commonly used sulfur and peroxides can be used,
and sulfur is preferred. The vulcanization agent can be used in an amount
preferably of about 0.1 to about 5 parts by weight and more preferably of
about 0.5 to about 3 parts by weight per 100 parts by weight of the
component (A).
Preferred vulcanization accelerators are of guanidine type, sulfenamide
type, thiazole type and the like. These can be used independently but
preferably in combination of two or more.
The rubber composition of the present invention is preferably used for
tires and most suitably for tire treads making use of characteristics that
the vulcanized rubber produced from this rubber composition has a high
wet-skid resistance and a low rolling resistance and is excellent in
processability because of absence of bleed on the surface.
Processes for producing tires including tire treads containing a vulcanized
rubber obtained by vulcanizing the rubber composition of the present
invention include a method in which an unvulcanized rubber containing the
rubber composition of the present invention is molded into a sheet with a
commonly used kneading machine such as rolls, kneader or the like and said
sheet is pasted on a tire base, placed in a mold having a tread pattern
and is vulcanization-molded by heating. The temperature for
vulcanization-molding is preferably about 100.degree. to about 250.degree.
C. and more preferably about 130.degree. to about 200.degree. C.
The complete disclosure of the priority document, Japanese patent
application number 07-91188 (filed Apr. 17, 1995), is incorporated herein
by reference.
EXAMPLES
The present invention will now be illustrated in further detail by means of
Examples which, however, should not be construed as a limitation upon the
scope of the invention.
Examples 1-8 and Comparative Examples 1-7
Into a 20 L SUS reactor substituted by nitrogen gas were charged 15 L of
n-hexane, 195 g of tetrahydrofuran, 1420 g of 1,3-butadiene, 580 g of
styrene and 8.7 mmol of n-butyllithium, which were reacted at a
temperature of 65.degree. C. for 4 hours. After adding 1.3 mmol of
tetrachlorosilane, the mixture was further reacted for 30 minutes. Then,
10 ml of methanol and 10 g of Sumilizer BHT were added and dried by vacuum
to obtain about 2200 g of solution polymerized SBR (A1).
Into a 1,500 ml Banbury mixer adjusted to 110.degree. C., were concurrently
charged the ingredients shown in Table 1, 50 parts by weight of X-140 (an
oil manufactured by Kyodo Sekiyu) and 6.4 parts by weight of Diablack N339
(HAF carbon black manufactured by Mitsubishi Chemicals), which were
kneaded at a revolution number of rotor of 150 rpm for 5 minutes. After
adding 1.5 part by weight of Sunknock N (an antioxidant manufactured by
Outi Shinko Kagaku), 1.5 part by weight of Antigen 3C (an antioxidant
manufactured by Siumitomo Chemical Co., Ltd.), 2 parts by weight of zinc
oxide and 2 parts by weight of stearic acid as the common combination, the
kneading was continued using an 8 inch open roll adjusted to 85.degree. C.
Then, 1 part by weight of Sox CZ (a vulcanizing accelerator manufactured
by Sumitomo Chemical Co., Ltd.), 1 part by weight of Sox D (a vulcanizing
accelerator manufactured by Sumitomo Chemical Co., Ltd.) and 1.4 part by
weight of sulfur were added and the kneading was further continued using
an 8 inch open roll adjusted to 40.degree. C. to give a unvulcanized
compound. Said compound was subjected to press vulcanization at
160.degree. C. for 30 minutes to give a vulcanized rubber. The vulcanized
rubber was evaluated by the methods described below. The results are shown
in Table 1 and Table 2.
Comparative Example 8
The procedure in Example 2 was substantially repeated except that the
maximum temperature during the kneading was 180.degree. C. The obtained
composition was gelled and it was impossible to evaluate the obtained
composition.
Method of Evaluation
(1) Tear strength and Rubber elasticity (300% modulus)
These were measured according to JIS-K-6252. In the measurement of the tear
strength, and angle type sample with no cutting was used. For both the
tear strength and rubber elasticity (300% modulus), larger value means
that the mechanical strength is higher. In the present invention, tear
strength is preferably 50 kgf/cm.sup.2 or more and rubber elasticity (300%
modulus) is preferably 120 kgf/cm.sup.2 or more.
(2) Rolling resistance (tan .delta.) index
A tan .delta. temperature dispersion curve was obtained by plotting valued
measured under the conditions of a frequency of 10 Hz, an initial strain
of 10%, a vibration amplitude of .+-.0.25% and a rise in temperature of
2.degree. C./min according to JIS-K-6394 except using Rheolograph Solid
L1R (manufactured by Toyo Seiki) and a sample of 50.times.5.times.2 (mm)
in length.times.width.times.depth. Values of tan .delta. at 0.degree. C.
and 60.degree. C. were obtained from this curve. The values of tan .delta.
in Examples and Comparative Examples are expressed by indices taking the
value in Comparative Example 1 as 100. Larger tan .delta. index at
0.degree. C. means that the wet-skid resistance is larger and a smaller
tan .delta. index at 60.degree. C. means that the rolling resistance is
lower, indicating that excellent properties are obtained when used for
tires or the like. In the present invention, tan .delta. (0.degree. C.)
index is preferably 105 or more and tan .delta. (60.degree. C.) index is
preferably 90 or less.
TABLE 1
__________________________________________________________________________
Example
Composition (wt)
1 2 3 4 5 6 7 8
__________________________________________________________________________
(A)
Kind *1 A1 A1 A1 A1 A1 A1 A1 A1
Amount (Part
100 100 100 100 100 100 100 100
by wt)
(B)
*2 Amount
78.5
78.5
78.5
78.5
78.5
78.5
78.5
78.5
Part by wt)
(C)
*3 Amount
6.4 6.4 6.4 6.4 6.4 6.4 6.4 4.5
(Part by wt)
(D)
Kind *4 D1 D1 D1 D2 D3 D1 D1 D1
Amount (Part
2 5 10 5 5 10 10 10
by wt)
Maximum Temp. during
150 150 150 150 150 130 160 130
Kneading (.degree.C.)
Evaluation
Tear strength
54 55 60 59 56 52 56 55
(kgf/cm.sup.2)
300% Modulus
167 177 180 163 143 121 176 123
*kgf/cm.sup.2)
Tan .delta. (0.lambda.C)
119 120 118 114 107 113 119 116
Tan .delta. (60.degree. C.)
84 81 72 84 89 81 72 73
Bleed on surface of
absent
absent
absent
absent
absent
absent
absent
absent
vulcanized rubber
__________________________________________________________________________
TABLE 2
__________________________________________________________________________
Example
Composition (wt)
1 2 3 4 5 6 7
__________________________________________________________________________
(A)
Kind *1 A1 A1 A1 A1 A1 A2 A2
Amount (Part
100 100 100 100 100 100 100
by wt)
(B)
*2 Amount
78.5
78.5
78.5
78.5
78.5
78.5
78.5
Part by wt)
(C)
*3 Amount
6.4 6.4 6.4 6.4 6.4 6.4 6.4
(Part by wt)
(D)
Kind *4 D1 D1 D4 D1 D1
Amount (Part
0 20 30 10 10 0 10
by wt)
Maximum Temp. during
150 130 144 130 115 123 125
Kneading (.degree.C.)
Evaluation
Tear Strength
54 52 47 52 51 28 77
(kgf/cm.sup.2)
300% Modulus
123 140 122 147 97 41 46
*kgf/cm.sup.2)
Tan .delta. (0.lambda.C)
100 125 131 92 105 42 47
Tan .delta. (60.degree. C.)
100 66 58 77 79 141 94
Bleed on surface of
absent
present
present
present
absent
absent
present
vulcanized rubber
__________________________________________________________________________
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